This invention relates to a process and apparatus for the annealing of steel annealing material, especially high-grade steel, in continuous units under a protective gas, wherein the annealing material in the protective gas atmosphere is successively heated, annealed, and cooled. (By steel annealing material is meant steel in any form which is to be annealed and will be referred to hereinafter as "raw steel").
The annealing of the raw steel is often conducted in a continuous manner in continuous units or a furnace under a suitable protective gas, often under gaseous atmospheres having a relatively high hydrogen concentration. In such a system, a problem exists in that according to new findings, boron contained in the raw steel is oxidized out of it during the annealing process, and the resultant gaseous boron oxide is later precipitated in the form of white dust in the downstream condensers serving to cool the annealed steel. The cooling efficiency of the condensers is so drastically reduced within a period of weeks that the unit has to be shut down so that the condensers can be replaced or cleaned. This leads to a production loss of at least one working day.
The problem of white dust is described, for example, in "Stahl und Eisen" 107 (1987), No. 6, pp. 267-273, especially p. 271, lower right. There, the problem of the heat exchangers clogged by white dust is solved or reduced by providing an installation wherein the heat exchangers can be subjected to a relatively quick cleaning or a quick exchange. Nevertheless, there is a need for further improvement.